Earth boring drill bits, such as polycrystalline diamond composite insert drag bits are used for drilling earth formations. For optimum drilling efficiency, the design of the bit is tailored for the type of earth formation to be drilled. This requires that the earth formation be analyzed and a bit geometry be designed. Once the bit is designed, a mold must be built for forming the bit.
To save time, it has been suggested that the process of rapid prototyping be used to build a bit. See for example, U.S. Pat. No. 5,433,280. This process builds the bit a layer at a time. Each layer is bonded to previous layer. The bonding may be caused by sintering subsequent layers together. This layer by layer sintering results in a bit that is weaker than a bit conventionally formed using a mold.
Rapid prototyping techniques, as the name suggests, are used to develop a prototype which has been designed in three dimensions using a computer aided design (CAD) system. These prototypes are used to evaluate the design and do not have the precise tolerances that are required of bits. As a result, a bit manufactured using this process may have to be machined to proper tolerances.
Accordingly, a process for building a bit is desired that reduces the time required to build a bit after a formation to be drilled has been analyzed, that uses existing bit materials, and which provides for precise tolerances.
This invention relates to a method for forming a mold which is used to form earth boting bits, such as polycrystalline diamond compact (PDC) insert drag bits. Once an earth formation to be drilled is analyzed, a three dimensional solid model of the bit is designed using a computer aided design (CAD) system. The system feeds the geometry data of the bit design to a layering device. The layering device divides the solid model in thin cross-sectional layers (also referred herein as CAD layers) revealing a cross-sectional outer mold line. It then proceeds to build the mold a layer at a time, such that each layer defines an inner mold line which is identical to the outer mold line of a corresponding CAD layer. Materials to be used for forming the mold include sand, graphite, ceramics, clay, other refractory materials plastic, rubber and wax. With the exception of the plastic, rubber and wax, the mold materials may be coated with a binder or a resin which allows for the melting of the binder or resin for fusing the mold material to construct a green state mold. Fusing of the mold material to construct a green state mold or sintering of the mold material can be accomplished by exposure of the mold material to high temperatures or CO2 gas.
In one embodiment, a laser beam is used to trace a layer of mold material having a thickness equivalent to that of a corresponding CAD layer. The laser traces the mold material defining an inner mold line which is identical to the outer mold line of a corresponding CAD layer. The laser beam can sinter or fuse the mold material layer. In another embodiment, the layering device lays out a precise layer of mold material defining an inner mold line identical to the outer mold line of a corresponding CAD layer. With this embodiment, each subsequent layer is exposed to a high temperature to either fuse or sinter the layers together. In a further embodiment, a model of the CAD bit design is built by the layering device using wax. The wax model is suspended in a mold casing in which is poured a mold material. The mold material is then cured to a green state and the wax is heated to a gaseous state so that it evaporates revealing the mold.
In yet a further embodiment, the layering device is used to construct reusable flexible formers using a flexible i.e., plastic or rubber material. The formers are used to form a mold or portions of a mold which is then used to form the bit.
In an alternate embodiment, the layering device is used to construct a master bit from preferably rubber or plastic. The master bit is then used to form molds from which are formed the bit bodies.
Once a mold is formed, a powdered steel or tungsten bit material is poured into the mold and is press molded or infiltrated with a binder to form the bit.